A Review of Measurement Techniques for Ortho-Para Hydrogen Catalytic Conversion Based on Raman Scattering Spectroscopy

Ortho-para hydrogen conversion is a key process in hydrogen liquefaction that reduces energy consumption and improves storage efficiency. Understanding the catalytic reaction kinetics and achieving real-time concentration monitoring are crucial for optimizing liquid hydrogen production. Among available techniques, Raman spectroscopy enables rapid, accurate, and efficient in situ measurement of ortho-para hydrogen concentration. Compared with traditional indirect methods that use gas chromatography, this technique meets the dynamic detection needs of the process and provides precise measurements, such as reaction kinetics, making it an advanced measurement technique. This study reviews the Raman scattering spectroscopy-based ortho-para hydrogen concentration measurement technique. Accordingly, the principle and composition of the optical detection system for this measurement technique are systematically explained. This study highlights the advantages and disadvantages of Raman spectroscopy compared with the methods of gas chromatography, nuclear magnetic resonance, and sound velocity by reviewing the development and evolution of the ortho-para hydrogen conversion measurement technique from its early use for macroscopic thermal conductivity measurements to its use for modern, in situ spectroscopic analyses. Finally, the study highlights the advantages of Raman spectroscopy in terms of its self-calibration and nondestructive, in situ, and rapid response capabilities. Overall, this study provides a theoretical basis and technical reference for the high-precision monitoring of ortho-para hydrogen in large-scale applications of hydrogen energy.